Generally, fluid machines have a seal mechanism for preventing a fluid from leaking out of a high-pressure space into a low-pressure space. For example, a centrifugal pump, which typifies fluid machines, has a seal mechanism for sealing a liquid at a mouth ring of an impeller and at a portion through which a main shaft or a shaft sleeve penetrates a body of the centrifugal pump. FIGS. 1 through 3 show an arrangement of a conventional seal mechanism. FIG. 1 is a plan view of a conventional seal mechanism 100, FIG. 2 is a cross-sectional view taken along line II-II of FIG. 1, and FIG. 3 is a cross-sectional view showing the conventional seal mechanism 100 together with an impeller 110 of a centrifugal pump.
As shown in FIG. 2, the conventional seal mechanism 100 includes a housing (or casing) 101 and a liner ring 102 received in the housing 101. As shown in FIGS. 1 and 2, the liner ring 102 has a plurality of notches 103 formed at equal intervals in a circumferential direction on a peripheral portion of the liner ring 102. In the example shown in FIG. 1, the liner ring 102 has three notches 103. The housing 101 has bent portions 104 formed on an inner circumferential portion of the housing 101. The bent portions 104 engage with the notches 103 of the liner ring 102 and serve as stoppers to prevent the liner ring 102 from being rotated.
The housing 101 has an inside diameter D1 larger than an outside diameter D2 of the liner ring 102 (D1>D2). Thus, the liner ring 102 is movable in a radial direction by a difference (D1−D2) between the inside diameter D1 of the housing 101 and the outside diameter D2 of the liner ring 102. The liner ring 102 is also movable in a circumferential direction by a difference between the width of the notches 103 and the width of the bent portions 104.
In the centrifugal pump shown in FIG. 3, the conventional seal mechanism 100 is attached to a body 111 of the centrifugal pump so that the housing 101 of the seal mechanism 100 is fitted into an innermost portion of the body 111 near the impeller 110. The impeller 110 is rotatable about an axis 112 as shown by arrow B. Accordingly, a handled liquid flows inside the impeller 110 as shown by arrows C. Thus, the centrifugal pump produces a space L having a low pressure below the housing 101 of the seal mechanism 100 and a space H having a high pressure above the housing 101 of the seal mechanism 100.
With the conventional seal mechanism 100, when the impeller 110 is rotated, it has previously been thought that a clearance δ (see FIG. 2) between an upper surface 101a of a bottom of the housing 101 and a lower surface 102a of the liner ring 102 becomes zero because the liner ring 102 is pressed against the housing 101. However, the clearance δ does not become zero in practical use because the handled liquid flows between inner surfaces of the housing 101 and outer surfaces of the liner ring 102 as shown by arrows E in FIG. 2. Thus, the liner ring 102 plays within the housing 101 together with the impeller 110, thereby causing noise to be generated.
As described above, when the impeller 110 is rotated, the bent portions 104 of the housing 101 engage as stoppers with the notches 103 of the liner ring 102 so as to prevent the liner ring 102 from being rotated together with the impeller 110 due to sliding contact between the liner ring 102 and the impeller 110, the viscosity of the handled liquid present between the liner ring 102 and the impeller 110, and other possible factors. Thus, if the liner ring 102 moves together with the impeller 110, the liner ring 102 hits the bent portions 104 thereby generating noise.